Hang on - someone with strength 4 can walk around carrying 159 kg without penalty?! That's... that's a heck of a lot.
And someone with Strength 1 is taking stun damage walking down the street carrying 11 kg? That's not just weak; that's enfeebled. You can be well below average strength and carry that weight around without being at risk of collapsing. This renders Strength 1 characters all but unplayable.
In my experience very few games have encumbrance math that is even moderately realistic, but that is the math we have to work with.
While I personally would still use it (only because I tend to be a by the book kind of guy), I'd still much rather see the value of focusing on Strength increased as opposed to incentivizing it by overpenalizing dumped stats.
However, if you put Strength to 1, you can be easily overwhelmed in grappling combat
To me, this is the only valid argument for why one should not dump strength. Grappling is savage in this edition.
But that said, it is also very easy to build a character that the grappler will just never hit, so there is always that. Full defense, block, dodge, combat sense, ect. are good ways to ensue you most likely avoid the one attack you don't want to land.